Conventional Power Factor Correction (PFC) uses a rectifier bridge followed by a separate boost stage. Such boost converters produce a relatively high voltage which is filtered and stored in a capacitor. A subsequent power stage reduces the voltage and regulates the output. Conventional PFC circuits operate in Discontinuous Conduction Mode (DCM), Continuous Conduction Mode (CCM), or Critical Mode. Each mode of operation has advantages and disadvantages, but changing from one mode to another is difficult or impossible for a particular controller. Further, these circuits are limited to matching input current to AC line voltage, and are not suited for applications which require more flexible control of input current.
U.S. Pat. No. 4,974,141, Severinsky et al, and U.S. Pat. No. 7,202,640 B2, Morita, teach single stage power converters with both regulation and improved PFC. Those devices rely on the output capacitance to filter line frequency ripple. That filter capacitance must then be much larger than in the usual case where only the much higher switching frequency need be filtered. Very large output capacitors are bulky and expensive and limit the agility of a power converter. AC output voltage or current is not feasible for power converters requiring large output filter capacitors.